The invention concerns the removal of dead tissue from a wound and more particularly, a bandage that promotes the removal of dead tissue by substances that the body itself produces.
Chronic wounds are a common aliment, afflicting over 5 million people annually in this country. The majority of chronic wounds are caused by a local or generalized vascular insufficiency that reduces blood flow to the skin and subcutaneous tissue. The most common type of chronic wounds include: pressure ulcers (decubiti, or "bed sores"); diabetic ulcers; arterial ulcers; venous ulcers, or a combination of these. Chronic wounds are full-thickniess skin injuries that may be very large and that may persist for months or years.
The treatment of chronic wounds presents may challenges. First, chronic wounds frequently exude large olumes of fluid. In the case of venous leg ulcers or pressure ulcers, this fluid may primarily be a serious transudate consisting of plasma and interstitial fluid. In the case of an infected or heavily colonized wound or a wound with necrotic (dead) tissue, the fluid will contain many white blood cells, cellular debris, and toxic cellular metabolic waste products. Such fluid is commonly denominated as "exudate" or "pus".
Historically, the philosophy of wound management has encouraged drying a wound. To promote drying, a wound would be covered with a simple absorbent gauze, or left open to the air to dry. At times, heat may have been applied to the wound to enhance drying. It is now recognized that drying the wound can actually inhibit healing.
Currently, the goal of wound management is to keep a wound moist. This may be accomplished by trapping exudate or transudate in a wound bed under a substantially fluid-impermeable bandage. This practice avoids drying a wound, but leads to a new problem. In this regard, larger amounts of fluid from moderate or heavily exudating wounds may result in a pool of trapped fluid under the bandage. This pool of fluid is in constant contact with the wound and the peri-wound skin, which is a margin of skin that surrounds and abuts the wound. As a result, the wound and peri-wound tissues are constantly wet, which can lead to maceration and further damage. Additionally, the fluid contains cellular debris and metabolic waste products that may be toxic to the living tissue of the wound bed and peri-wound. The toxicity of the fluid may retard wound healing and, indeed, may damage healthy peri-wound tissue and already healed wound tissue.
Consequently, there is a need for a device that maintains an environment of high humidity over a wound in order to prevent evaporative drying of the wound while, at the same time, managing the excess fluid to keep it away from the peri-wound skin and the wound bed. In short, there is a need for a device that will keep a wound area humid, but not wet.
One significant advantage to be gained by use of such a device would be optimization of autolytic debridement. Autolytic debridemenet denotes the body's natural ability to break down dead tissue, thereby continuously cleaning a wound so that new skin cells can grow to fill and cover the wound, thereby promoting its healing. In this regard, "autolytic" refers to the destruction of dead tissue by agents produced by the body. "Debridement" is the removal of dead cells or tissue from a wound. Autolytic debridement is therefore the breaking down and removal of dead tissue from a wound by substances and processes that are natural to the body. This function is carried out by white blood cells generally known as phagocytes, and by a variety of enzymes. In the process the phagocytes die and add to the cellular debris of the necrotic tissue in the exudate fluid. The exudate fluid flows away from the wound, thereby removing the dead cells and other debris. Autolytic debridement under prior art wound bandages is usually ineffective at cleaning wounds because the exudate fluid collects and pools in the wound. Clinicians must frequently intervene by resorting to repeated surgical debridement in order to clean necrotic tissue from a wound. There is a need therefore to support and enhance autolytic debridement by removing exudate with its toxic waste by-products from the wound area.
Since autolytic debridement is an autogenic process, driven by the functioning of body systems, it is affected by temperature. In this regard, hypothermia is known to slow or even stop cellular functions, immune system functions, enzyme reactions, and biochemical processes. Effective phagocytosis requires an active immune system, active cellular functions, and rapid enzyme and biochemical reactions. Many wounds, because of their locations on body limbs, are hypothermic. The cool environment of these wounds slows down the process of autolytic debridement, extending the time required for healing.
Accordingly, the need for a device to keep a wound area humid, but not wet, is compounded by the need for the device to enhance autolytic debridement by carrying exudate away from the wound and keeping the wound warm.